While the threaded fastener of the present invention, in the form of a bolt or screw, is capable of cutting new threads in an appropriately sized unthreaded bore, it is particularly adapted to recut threads in a previously threaded bore wherein the threads have been damaged or stripped. For purposes of an exemplary showing, the fastener of the present invention will be described in terms of this application thereof.
Prior art workers have devised a number of bolt-like fasteners for this vary purpose. U.S. Pat. Nos. 2,096,937; 2,738,698; 1,823,574; 3,492,908; 4,449,874 and 5,000,639 are exemplary.
All of the above-listed references, with the exception of U.S. Pat. No. 4,449,874, provide one or more cutting edges at the lead-in end of the fastener. The cutting edges are formed by grooves which extend through the lead-in end of the fastener and conduct metal cuttings into the bore being rethreaded. The above-noted U.S. Pat. No. 4,449,874 differs in that it is provided with a longitudinal slot which is spaced from the lead-in end of the fastener. That end of the slot nearest the lead-in end of the fastener is provided with a first hole which extends transversely through the fastener. This transverse hole is intersected by a second axial hole which extends from the transverse hole through the lead-in end of the fastener. As a consequence, the two holes serve to form a passage directing metal cuttings into the bore being rethreaded. Thus, even though the cutting edge, formed by the longitudinal slot, is spaced from lead-in end of the fastener, the first and second holes still provide a passage for metal cuttings to enter the bore.
The present invention is based upon the discovery that a number of advantages can be realized if the metal cuttings are collected, retained and compacted within a slot in the fastener. To this end, the fastener of the present invention comprises a threaded shank terminating in a lead-in end and a headed end. The shank is provided with a longitudinally extending slot slightly deeper than the threads and extending from the first thread adjacent the lead-in end toward the headed end. That end of the slot nearest the lead-in end of the fastener includes a transverse bore which extends radially inwardly of the shank toward, but not beyond the shank longitudinal axis.
As the fastener of the present invention is turned into the bore to be rethreaded, the trailing longitudinal edge of the slot constitutes a cutting surface and metal cuttings formed as a result of the thread cutting operation are collected, retained and compacted in the slot and its axial bore.
As a consequence of this structure, the fastener of the present invention captures all of the metal cuttings and prevents them from entering the bore. This eliminates damage to the threads caused by the cuttings. It further eliminates the possibility of the cuttings causing binding and increasing the torque requirement to the extent that the fastener, itself, could break. The faster of the present invention is characterized by increased strength, as compared to a fastener of the type taught in U.S. Pat. No. 4,449,874, since it does not have an axial hole, or a transverse hole which extends through the entire fastener. It has further been found that containment and compacting of he metal cuttings will have a locking effect on the fastener when fully seated in the bore, resisting loosening of the fastener by virtue of vibration and the like.